1. Field of the Invention
The present invention relates to a magnetic bubble store. It applies to the storage of binary information in the form of separate magnetic domains, called bubbles, in a layer of magnetic garnet. These domains have a magnetization which is the reverse of that of the magnetic garnet.
2. Description of the Background
Each bubble can be displaced by a force and the movement of the bubble can take place freely in any random direction in the plane of the magnetic garnet layer. The bubbles are formed in the garnet layer by applying a continuous magnetic field thereto perpendicular to the plane of the layer. In practice, the field is produced by a permanent magnet and ensures the non-volatility of the information contained in the store. The magnetic garnet layer in which the bubbles are formed is generally supported by an amagnetic monocrystalline garnet.
It is known to displace bubbles contained in the magnetic garnet by means of conductive strips or sheets traversed by currents and having windows making it possible to fix the course of the bubbles in said garnet. These sheets are electrically insulated from one another and from the garnet. It is also known to displace the bubbles in the garnet by means of a rotary magnetic field, said bubbles being guided along the boundaries of patterns defined by the ion implantation zones of said garnet. In both cases, the bubbles are displaced as in a shift register. The information constituted by the garnet is displaced for each rotation of the rotary magnetic field or each current pulse cycle in the conductive sheets or strips. This organization in shift register form is the most widely used. The reading of an information contained in the store requires a number of displacements dependent on the number of positions which said information has to traverse in the shift register for it to pass from the position in which it is located up to the end of the register. Thus, this organization requires very long access time and access is then said to be "sequential", because access to the information is a series access necessitating sequences, either in the form of rotations of a rotary field, or of pulses in perforated sheets traversed by a current.
The present invention is more particularly directed at bubble stores in which the bubbles are displaced as a result of currents traversing the perforated conductive sheets. In per se known manner, such a store generally has two conductive sheets in which there are windows. These sheets are parallel to one another and are traversed by parallel currents. The bubbles can be transferred between two cells of memories reference marked by windows by a displacement perpendicular to the currents traversing each of the strips in which these windows are formed. The bubbles can also be displaced between two storage cells designated by windows, as a result of currents parallel to the displacement direction of the bubbles. The currents are nevertheless parallel to one another in the two sheets for displacements parallel or perpendicular to the currents. A known store of this type is described in U.S. Pat. No. 4,134,358. In the store described in this patent, the superimposed conductive sheets are respectively traversed by parallel currents and the displacements of the bubbles in the store are perpendicular to the direction of said currents for storage or minor registers, whilst the displacements are parallel to these currents in the major or access register.
This known type of bubble store, in which the conductive sheets are traversed by parallel currents has the major disadvantage of only permitting an organization of the store in the form of storage or minor registers and access or major registers, the access to the information in the store can only be sequential. With this type of store, it is not possible to obtain direct access in a first phase to a matrix of cells of said store and then obtain access in a second phase to each of the cells of the matrix in a sequential manner, in order to bring about a pseudorandom access. This type of store also suffers from the advantage of making impossible a random access to the cells of said store, in order to modify the information contained therein, by simply modifying the direction of the currents circulating in the conductive strips, and without requiring sequential actions.